1. Field of the Invention
This invention relates to a brush assembly used in dynamoelectric machines for the transfer of current from a stationary brush magazine to a rotating contact part with stationary brush boxes, which mechanically and electrically are connected with the supporting structure, to receive and radically guide the brushes whereby the brushes are removable for control and replacement purposes while the machine is running and under voltage.
2. Description of the Prior Art
A brush assembly of the above noted type is, for example, known from the U.S. Pat. No. 3,387,155.
Uninterrupted operation assumes priority importance with machine units which become bigger and bigger, particularly with turbogenerators and hydrogenerators. If such machines are equipped with brushes, the shutting-down, solely for the purpose of inspecting the brushes or exchanging worn brushes, is undesirable since any shutting-down results in a considerable reduction in production. For this reason, different brush holder arrangements have been created in the recent past which permit exchanging the brushes while the machine is running and under voltage.
In the case of some of these known assemblies, always one brush with a respective supporting brush box and pressure mechanism, which presses the brush against the rotating contact part (slip ring, commutator), is separated from the stationary contact part, from the supporting structure or from the brush gear bars. The electrical connection is also interrupted with the mechanical separation. Plug brush holders of this kind are, for example, described and shown in the U.S. Pat. No. 3,466,481 and in the Swiss Pat. No. 504,797. While with these designs always only individual brushes, together with the supporting brush box or pressure mechanisms, can be exchanged, other known assemblies provide for combining several brushes with their boxes and spring arrangements which are detachable as a unit.
An essential feature of all these designs is that not only the brush, the only part of importance, but also the brush guide elements (brush box), the pressure system (spring) and the fastening means are combined to form a "brush holder plug-in unit" which can be pulled off while the machine is running. An advantage of the plug-in units with several brushes is a considerably faster inspection and a faster exchange of worn carbons which plays an essential role especially in case of machines with up to 100 and more brushes.
In case of high speed dynamoelectric machines, particularly turbogenerators, turboexciters and homopolar generators, an essential requirement of the brush system is that the brush holder box guiding the brush must be designed in a vibration-resistant manner and must be rigidly connected with the resting part of the supporting structure. This requires an extremely rigid construction and a strong fastening mechanism for the known plug-in units, especially for those with several brushes. The plug-in units therefore are necessarily voluminous, heavy and inconvenient in their handling. Additionally, the space they occupy cuts down on the cooling flow cross-sections necessary for the supply of cold air. The space requirement of such plug-in units becomes especially serious for large turbogenerators where the necessary number of brushes can practically not be accommodated on the slip rings limited by other frame conditions.